A conventional car audio system typically includes a microprocessor, a tuner, a tape or CD player, an equalizer, a power amplifier and speakers. The microcomputer controls the audio system in accordance with user's manipulations. The equalizer compensates for frequency characteristics of the output audio signals as desired by the user. A typical equalizer includes a first equalizer connected to a front right speaker, a second equalizer connected to a front left speaker, a third equalizer connected to a rear right speaker, and a fourth equalizer connected to a rear left speaker.
In conventional car audio systems, however, the reproduced acoustic phases of the respective speakers within the car are different from each other, thereby causing offsets. For example, a phase inversion occurs between the reproduced sounds of the front speakers and the rear speakers of the car. Due to this phenomenon, a sound offset occurs to a severe degree. Particularly, in a frequency band of less than 100 Hz, the sound offset phenomenon is most problematic. Further, due to the sound offset phenomenon, the user tends to forcibly boost the audio signals in a frequency band of less than 100 Hz through the equalizers. As a result, the audio signals are distorted, degrading the sound quality and causing vibration in the car body panel.